The present invention is an improvement on sea wave energy conversion apparatus of the kind described in U.S. Pat. No. 4,152,895, which issued on May 8, 1979 on an invention by Leslie S. Wirt.
The energy in sea waves in mid-ocean is approximately half kinetic and half potential. However, when encountering a sloping beach, the sea waves steepen and crest, and finally break into pulses of translationally rushing water having primarily kinetic energy. The water rushing onto the beach is technically no longer a "wave" in the sense of exhibiting undulatory motion, but nevertheless is customarily referred to in the literature as "the primary wave of translation". A sloping beach thus converts the energy in successive sea waves into pulses of kinetic energy.
If a sea wave encounters a beach having a generally umbrella-shaped or mushroom-shaped configuration as in the case of a generally circular island atoll, the incident wavefront is refracted by the beach in accordance with Snell's Law, as discussed, e.g., by R. S. Arthur in "Refraction of Water Waves by Islands and Shoals with Circular Bottom Contours," Transactions American Geophysical Union, Vol. 27, No. II, 1946. For typical ocean waves occurring in a costal zone around an island atoll, most of the wavefronts are refracted so as to assume generally spiralling paths around the atoll before breaking on the beach. The pulses of rushing water produced when the spiralling wavefronts break thus travel along paths that tend to converge at the interior of the atoll.
In accordance with the above-referenced Wirt patent, which is incorporated herein by reference, a man-made circular atoll having a central aperture is positioned to intercept energy-laden sea waves. The contour of the atoll beach causes successive sea waves impinging thereon to be refracted so as to acquire a spiralling motion while steepening and cresting. The cresting waves then break into pulses of translationally rushing water, which converge toward the central aperture. Guide vanes are mounted on the atoll to channel the pulses of rushing water into the central aperture with a swirling motion. A vertical standpipe of generally cylindrical configuration is connected to the atoll to receive the rushing water passing through the central aperture. The standpipe is filled with water, which acquires angular momentum due to angular impulses imparted thereto by the swirling motion of the pulses of rushing water entering the standpipe as successive sea waves impinge upon the atoll.
The kinetic energy of the pulses of rushing water produced as successive sea waves break on the atoll beach is stored in the angular momentum of the water in the standpipe. For this reason, the water in the standpipe is characterized as a "liquid flywheel." A turbine and attached shaft having a common rotational axis are positioned inside the standpipe, with the rotational axis of the turbine and shaft substantially coinciding with the cylindrical axis of the standpipe. The angular momentum of the water in the standpipe causes the turbine and shaft to rotate. An electrical generator is coupled to the shaft, so that the rotational energy acquired by the shaft is converted by the generator into electrical energy.
The turbine creates a pressure differential at the outlet of the standpipe. It is therefore preferable to provide a discharge diffuser at the standpipe outlet in order to obtain more efficient radial outflow of water from the standpipe, thereby facilitating entry of subsequent pulses of rushing water into the standpipe via the guide vanes as successive sea waves break on the atoll beach.
Until the present invention, however, the effect of sea state variations and tidal conditions on the efficiency of energy conversion provided by a circular atoll type of apparatus as described in the Wirt patent had not been fully recognized. For that reason, no provision was made in the prior art for adjusting a sea wave energy conversion apparatus of the circular atoll type to varying sea state and tidal conditions in order to maximize electrical power output.
Also, until the present invention, no provision was made for adjusting a sea wave energy conversion apparatus of the circular atoll type in order to obtain maximum electrical power output irrespective of changes in efficiency of the turbine or of the electrical generator. Furthermore, until the present invention, a sea wave energy conversion apparatus of the circular atoll type could not be submerged on command in order to minimize exposure of the apparatus to the damaging effects of violent storms.